GCN Circular 22678

E. Bissaldi (Politecnico & INFN Bari)
reports on behalf of the Fermi GBM Team:


"At 10:37:03.04 UT on 27 April 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180427A (trigger 546518228 / 180427442).
The on-ground calculated location, using the GBM trigger data, is

RA = 283.33, Dec = +70.30

(J2000 degrees), with an uncertainty of 1 degree (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ).

The angle from the Fermi LAT boresight at the GBM trigger time is 136 degrees.

The GBM light curve shows a single FRED-like emission episode
with a duration (T90) of about 26 s (50-300 keV).
The time-averaged spectrum from T0 to T0+26 s is
best fit by a Band function with Epeak = 108 +/- 3 keV,
alpha = -0.28 +/- 0.04, and beta = -2.81 +/- 0.07.

The event fluence (10-1000 keV) in this time interval is
(4.92 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+5.3 s in the 10-1000 keV band
is 29.2 +/- 0.8 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."